1. Field of the Invention
The present invention relates to water-based inks.
2. Description of the Related Art and Brief Description of the Invention
Diarylide pigments represent an important class of coloring agents used primarily in the manufacture of inks. The most utilized diarylide pigments include, but are not limited to, the following: Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 17 and Pigment Yellow 83.
It is documented in the prior art literature that the addition of fatty primary amines to an aqueous slurry of Pigment Yellow 12, followed by filtration and drying at an elevated temperature, results in a pigment having superior properties (e.g., increased strength, gloss, transparency, and lower rheology) when used to make a solvent-based printing ink, especially a publication gravure type ink. (B.P. 1,080,835). There are many variations on this technology which have also been patented. Some include the use of diamines to reduce penetration (E.P. 57,880), the use of rosin amine (B.P. 1,080,116; B.P. 1,288,044), the use of heterocyclic amines (B.P. 1,334,570), etc. There are also many patents on the process of forming the azomethine additive (aka Schiff's Base or ketimine).
Thus, some patents include pre-reaction of the amine and the acetoacetanilide, followed by reaction with tetrazotized DCB (B.P 1,334,570; U.S. Pat. No. 4,643,770). Others utilize reaction of the dry Pigment Yellow 12 in a solvent to form the azomethine (U.S. Pat. No. 4,468,255), but most, simply form the additives by drying the presscake containing the amine.
Although the use of the numerous aforementioned amine treatments afford pigments with improved application properties in solvent-based inks (e.g., publication gravure, nitrocellulose packaging, solvent flexo), the use of amine modification for water-based inks has not been exploited, and is within the scope of the present invention. Accordingly, it has been determined that by producing the azomethine compounds of the present invention, diarylide pigment compositions exhibiting significantly improved application properties in water-based ink and coating compositions can be obtained. This is of increasing importance with the current trend toward the use of water-based printing inks. The use of the products of this invention by affording stronger and improved diarylide pigments for water inks, offers significant economic incentives required for printers to change from the traditionally less costly solvent inks